1. Field of the Invention
The present invention relates to a low noise current buffer circuit and current voltage (I-V) converter, and more particularly, to a low noise current buffer circuit and current voltage converter capable of reducing impact of noise of a system voltage on an output voltage.
2. Description of the Prior Art
A current voltage converter, such as a bandgap reference circuit, utilizes a current source to output an input current to an output resistor to generate a required output voltage. In such a conventional structure, since the current source likely experiences interference from noise of a system voltage, the output voltage is affected and can not stay within a stable range.
Please refer to FIG. 1A and FIG. 1B. FIG. 1A is a schematic diagram of a bandgap reference circuit 10 for generating a zero temperature coefficient (zero-TC) voltage in the prior art, and FIG. 1B is a schematic diagram of a bandgap reference circuit 12 for generating zero-TC current in the prior art. In the bandgap reference circuit 10, a transistor 102, which can be considered a current source, outputs an input current Iin to an output resistor Ro and a diode Q1, to generate a zero-TC output voltage Vout. Similarly, in the bandgap reference circuit 12, a transistor 104, which can be considered a current source as well, outputs an zero-TC input current Iin′ to an output resistor Ro′, to generate an output voltage Vout′. In such a situation, a system voltage VDD experiences interference from noise, and the input currents Iin, Iin′ experience interference as well, such that the output voltages Vout, Vout′ are affected, and thus can not stay within a stable range.
For example, when the system voltage VDD rises rapidly due to noise, the transistors 102, 104 output corresponding greater input currents Iin, Iin′, which increases the output voltages Vout, Vout′, such that the output voltages Vout, Vout′ are greater than the stable range. Thus, there is a need for improvement of the prior art.